how do i install this 3 port mac valve for boost control?

[kevboost7]

Hello everyone, i'm fairly new to the tuning/modifying scene and just picked up a r32 gtr. I purchased a 3 port mac valve for boost control and i have a haltech platinum pro ecu that i haven't installed yet. Right now, i have the intake plenum off as all my coolant lines are rotted so i replaced them with silicone hoses. I figured i'd get some other stuff out of the way, but i'm a little confused on the boost controller and where i should hook it up. 

I see diagrams on the web of people saying that i should connect it near the back of the engine for boost source. However, i still have the factory boost selonoid. Is it possible that i can just replace the factory one with the boost selenoid? 

 

And if so, which one is the in and which one is the out? 

 

[GTSBoy]

Don't install the MAC valve until you need it. The stock ECU wants the original boost control solenoid. It is possible to make the MAC do its job, but that's a f**karound that you'd just have to undo.

The stock boost control plumbing schema is readily visible in the factory service manual, which is easily downloaded. It picks up a boost signal from the plenum (I think, it's definitely upstream the throttles, anyway) and sends the boost signal on to the wastegate actuators.

The MAC valve plumbing is very simple. Boost reference from the same pre-throttle location as the original. One of the other ports is the outlet to the wastegates. The other is the vent. The MAC valve is just a 3 way valve that has one common port that is switched back and forth between the other two ports when it is energised/de-energised. There is a diagram on the side of the valve that shows you this. The boost source goes onto the common port. The wastegates are connected to the port that is fed from the common when the solenoid is not energised. The other port is the vent and should be connected back to the pre-turbo, filtered inlet duct (ie, after the AFM(s).)

There are literally dozens, if not hundreds of threads on here with diagrams. But the words above should be sufficient.

[joshuaho96]

4 hours ago, kevboost7 said:

Hello everyone, i'm fairly new to the tuning/modifying scene and just picked up a r32 gtr. I purchased a 3 port mac valve for boost control and i have a haltech platinum pro ecu that i haven't installed yet. Right now, i have the intake plenum off as all my coolant lines are rotted so i replaced them with silicone hoses. I figured i'd get some other stuff out of the way, but i'm a little confused on the boost controller and where i should hook it up. 

I see diagrams on the web of people saying that i should connect it near the back of the engine for boost source. However, i still have the factory boost selonoid. Is it possible that i can just replace the factory one with the boost selenoid? 

 

And if so, which one is the in and which one is the out? 

 

Didn't you post this question on Reddit already? If not here's my answer again:

https://www.gtrusablog.com/2013/02/rb26dett-vacuum-and-wastegate-diagram.html

Port 1 is the blue line. Port 2 is the green line. Port 3 is also the green line. The key point is that you will have to modify the vacuum line for port 3. Instead of tying port 2 and 3 together you cap the vacuum line on the combo coolant/vacuum pipe and the line on the plenum goes directly to the valve. Port 2 has unchanged routing.

As others have said don't do this until you get the new ECU installed and set up properly. Only do it once you're ready to set up boost control to reduce the number of variables.

[kevboost7]

@joshuaho96 thank you for the response. I did see that you answered my question on reddit, but i didn't know how credible it was, since it was on reddit haha.

I have a few more questions. The first one might be a dumb one, but how do i cap the vacuum line on the coolant/vacuum pipe? I'm assuming that you are referring to this pipe. Can you double check my drawing to see if i got this right?

and on the intake plenum, i would connect this line to port 3 on the mac valve? because this line would originally go to the "capped off" line on the water pipe.

 

And then lastly, would this already be capped off? or would i have to do this myself?

 

 

 

[joshuaho96]

3 hours ago, kevboost7 said:

@joshuaho96 thank you for the response. I did see that you answered my question on reddit, but i didn't know how credible it was, since it was on reddit haha.

I have a few more questions. The first one might be a dumb one, but how do i cap the vacuum line on the coolant/vacuum pipe? I'm assuming that you are referring to this pipe. Can you double check my drawing to see if i got this right?

and on the intake plenum, i would connect this line to port 3 on the mac valve? because this line would originally go to the "capped off" line on the water pipe.

 

And then lastly, would this already be capped off? or would i have to do this myself?

 

 

 

1. To cap the pipe buy one from an auto parts store, it looks like this: https://www.amazon.com/Assortment-Automotive-Carburetor-Manifold-Fitting/dp/B09B3N5DF1

Be sure to retain the hose clamp on the cap or it will pop off under boost. Your diagram showing the part to cap off is correct.

2. Yes, that port on the plenum would go to port 3. It’s also worth mentioning that you shouldn’t be using the back of the balance tube for a boost controller because it’s after the throttle body. The other two ports are already used for the cold start valve and the idle air control valve.

3. There’s no pressure port to measure on either turbo directly. That diagram is generic, not specific to the RB26. The port on the plenum is the pressure port and that’s the combined output of both turbos. So there’s nothing to cap. If you are concerned that the two turbos are not working equally that’s a known problem with the OEM intake piping and part of the reason why the rear turbo tends to blow up first.

[kevboost7]

4 hours ago, joshuaho96 said:

1. To cap the pipe buy one from an auto parts store, it looks like this: https://www.amazon.com/Assortment-Automotive-Carburetor-Manifold-Fitting/dp/B09B3N5DF1

Be sure to retain the hose clamp on the cap or it will pop off under boost. Your diagram showing the part to cap off is correct.

2. Yes, that port on the plenum would go to port 3. It’s also worth mentioning that you shouldn’t be using the back of the balance tube for a boost controller because it’s after the throttle body. The other two ports are already used for the cold start valve and the idle air control valve.

3. There’s no pressure port to measure on either turbo directly. That diagram is generic, not specific to the RB26. The port on the plenum is the pressure port and that’s the combined output of both turbos. So there’s nothing to cap. If you are concerned that the two turbos are not working equally that’s a known problem with the OEM intake piping and part of the reason why the rear turbo tends to blow up first.

Got it. Thanks so much man. You have no idea how much i was scratching my head at this earlier when i was in the garage. 

One last thing, i purchased these silicone vacuum hoses. You think they will be okay under the plenum? https://hpsperformanceproducts.com/products/hps-quarter-inch-red-high-temp-silicone-vacuum-hose-tubing-coolant-overflow-tube

 

The reason i'm asking is that they aren't reinforced like the new silicone coolant tubes i got. I'm just not sure if it will affect any performance or not.

Additionally, if the diameter of the vacuum hose that i use 1mm too small, is that going to be an issue?

 

[kevboost7]

5 hours ago, joshuaho96 said:

1. To cap the pipe buy one from an auto parts store, it looks like this: https://www.amazon.com/Assortment-Automotive-Carburetor-Manifold-Fitting/dp/B09B3N5DF1

Be sure to retain the hose clamp on the cap or it will pop off under boost. Your diagram showing the part to cap off is correct.

2. Yes, that port on the plenum would go to port 3. It’s also worth mentioning that you shouldn’t be using the back of the balance tube for a boost controller because it’s after the throttle body. The other two ports are already used for the cold start valve and the idle air control valve.

3. There’s no pressure port to measure on either turbo directly. That diagram is generic, not specific to the RB26. The port on the plenum is the pressure port and that’s the combined output of both turbos. So there’s nothing to cap. If you are concerned that the two turbos are not working equally that’s a known problem with the OEM intake piping and part of the reason why the rear turbo tends to blow up first.

i noticed with the silicone vacuum lines, they are often too small in diameter for the hoses, so they don't even fit. You sure that the hose clamps are necessary? cause they feel pretty snug already.

[Ben C34]

Losing a waste gate line isn't worth the cost and slight hassle of a hose clamp.

 

Engines die as a result of that.

[Murray_Calavera]

1 hour ago, kevboost7 said:

i noticed with the silicone vacuum lines, they are often too small in diameter for the hoses, so they don't even fit. You sure that the hose clamps are necessary? cause they feel pretty snug already.

The hoses can be bought in different sizes, just buy the correct size hose.

[GTSBoy]

Just spit on it.

[joshuaho96]

2 hours ago, kevboost7 said:

Got it. Thanks so much man. You have no idea how much i was scratching my head at this earlier when i was in the garage. 

One last thing, i purchased these silicone vacuum hoses. You think they will be okay under the plenum? https://hpsperformanceproducts.com/products/hps-quarter-inch-red-high-temp-silicone-vacuum-hose-tubing-coolant-overflow-tube

 

The reason i'm asking is that they aren't reinforced like the new silicone coolant tubes i got. I'm just not sure if it will affect any performance or not.

Additionally, if the diameter of the vacuum hose that i use 1mm too small, is that going to be an issue?

 

You don't need reinforced lines for vacuum lines. If you buy the OEM Nissan vacuum line it's just nitrile rubber with no reinforcement. Some hoses are reinforced but they're usually the larger ones like the AAC/IACV that have relatively thin walls compared to their inner diameter.

If the factory line uses a hose clamp then you need a hose clamp. Even some places like the FPR regulator where no hose clamp is specified I would recommend one anyways. The point of the hose barb is so once you get a hose clamp in place in order to pull the hose off the hose has to fight the spring force of the hose clamp in order to widen enough to slip off. As others have mentioned the failure mode of letting the wastegate line vent to atmosphere is catastrophic. This is equivalent to 100% duty cycle on the boost valve and usually means enough boost to blow up your engine. Hose clamps are cheap, especially compared to a new engine. If you're near the SF Bay Area I probably have a few left over I can give to you for free. Otherwise it's 16439-N210A from a Nissan dealer.

When it comes to engines 1mm off can be a pretty big deal. I would just get the right vacuum hose. Nothing about these engines is cheap and doing the intake manifold gaskets is enough of a PITA that you may as well do it right the first time.

[GTSBoy]

I call bullshit. On a 3mm straight steel pipe (unbarbed) with rubber or silicone hose pushed on more than ~15mm you wouldn't be able to expand the hose and apply enough force to get it to pop off the pipe with anything like the boost pressures available on a petrol engine.

Sure, use a hose clamp if it assuages your paranoia, but in reality it is absolutely unnecessary. That's why the OEM Nissan hose for the wastegate, the FPR, etc, have nonesuch. (And, yes, I realise it's only 0.5bar in most of those applications, but the reality extends waaaay up past 3 bar).

Small hose? Slightly too small? Spit on it, push it on, let the spit dry, forget your problems. Especially when we're talking small bore SILICONE hose, which is about a billionty times more forgiving of such abuse than nitrile. Remember, it took 25 years for your OEM Nissan rubber hoses to get old and die. The car we're talking about here will not even be able to be fuelled in another 20 years. If you do manage to find your own supply of ethanol, you'll have to put in an application in triplicate to the ecoNazi department of your local government for a permit to be able to take it out on the road without computer self-drive and you'll have to sign up to 150 hours of community labour to pay off the CO2 emissions penalty from your voluntary environmental vandalism. So there's no need to worry about this hose sneaking up on you and ruining your life/engine in the meantime.

[Duncan]

I've had a properly sized rubber hose without a clamp pop off the standard fittings, specifically the boost reference at the back of the post throttle balance tube which I was using for the Haltech MAP input, at 1.3 bar

I run cable ties on all of those small hoses for safety and reliability (they are too small for any sort of useful hose clamp, factory had those little spring clamps which are just a form of decoration)

[GTSBoy]

Yes, there are cable ties on mine too, to assuage my paranoia.

[BK]

8 hours ago, Duncan said:

I've had a properly sized rubber hose without a clamp pop off the standard fittings, specifically the boost reference at the back of the post throttle balance tube

That's why you should cut them off front and rear and tap a 1/16 or 1/8 npt thread into it so you can fit a proper barb or AN fittings. 

[kevboost7]

On 10/3/2022 at 9:45 PM, joshuaho96 said:

You don't need reinforced lines for vacuum lines. If you buy the OEM Nissan vacuum line it's just nitrile rubber with no reinforcement. Some hoses are reinforced but they're usually the larger ones like the AAC/IACV that have relatively thin walls compared to their inner diameter.

If the factory line uses a hose clamp then you need a hose clamp. Even some places like the FPR regulator where no hose clamp is specified I would recommend one anyways. The point of the hose barb is so once you get a hose clamp in place in order to pull the hose off the hose has to fight the spring force of the hose clamp in order to widen enough to slip off. As others have mentioned the failure mode of letting the wastegate line vent to atmosphere is catastrophic. This is equivalent to 100% duty cycle on the boost valve and usually means enough boost to blow up your engine. Hose clamps are cheap, especially compared to a new engine. If you're near the SF Bay Area I probably have a few left over I can give to you for free. Otherwise it's 16439-N210A from a Nissan dealer.

When it comes to engines 1mm off can be a pretty big deal. I would just get the right vacuum hose. Nothing about these engines is cheap and doing the intake manifold gaskets is enough of a PITA that you may as well do it right the first time.

@joshuaho96 Thanks man, i'm all the way on the other coast in North Carolina. I wish i was in cali though, you guys have better weather haha. 

 

But thanks for the response. I'm gonna try to do everything the right way and use the correct size hoses. One last question, where do i connect the 2 wires from the 3 Port Mac Valve? Would i connect it to the stock boost controller?

Edited October 6, 2022 by kevboost7

[kevboost7]

Also, this is kind of a weird question, but theoretically, could i leave this line in place and cap it off at the end? (this is the line that would go up into the intake plenum)

because once i have the intake plenum on, it will be impossible to add the vacuum cap. So this gives me the flexibility of using the stock boost controller. Since i still need to learn how to map my ECU to the 3 Port mac valve. 

I'm not sure if my explanation make senses. 

Edited October 6, 2022 by kevboost7

[Duncan]

Yes, you can block off the end of a hose instead of capping the nipple on the plenum, same same. For many years the standard way was a suitably sized bolt, hose clamped or cable tied in place. The right way to do it would be one of those vacuum caps straight on the nipple as posted above. It is not impossible to get to, you just need tiny hands and to hold your tongue right while you try and do it.

The Haltech expects a mac valve to be installed in the location of the stock wiring, so just cut that and wire in the new plug there. But as said in post 2, the standard ECU works differently and you may have issues if you switch the boost controller before you switch the ECU

[joshuaho96]

2 hours ago, kevboost7 said:

@joshuaho96 Thanks man, i'm all the way on the other coast in North Carolina. I wish i was in cali though, you guys have better weather haha. 

 

But thanks for the response. I'm gonna try to do everything the right way and use the correct size hoses. One last question, where do i connect the 2 wires from the 3 Port Mac Valve? Would i connect it to the stock boost controller?

Stock boost wiring is fine, it goes to the ECU. If you don't want to cut the plugs you can make an adapter from the OEM harness to the new boost solenoid. Contact Wiring Specialties to see what they can do in that regard. As others have mentioned you can just shove a bolt or something into the end of the hose to cap it off if you don't want to put a cap in at the pipe. Personally I'm a big fan of retaining OEM connectors where possible after seeing how much people want for new ones or how much Nissan wants for new harnesses now.

[kevboost7]

Thanks everyone for the responses. I was able to put my intake plenum back on with the new coolant hoses and everything is working great! 

I now have a question regarding the 3 port mac valve and the difference between, that and a boost controller. Some Boost controllers i've seen has an external display with a knob that you can turn up the boost...

Do I need a boost knob?